High pressure pumps are disclosed in JP-A-2002-54531 and JP-A-2003-35239 (US 2003/0017069A1, US 2004/0096346A1). In these high pressure pumps, fuel is introduced from a low pressure pump or the like into an inlet chamber through a fuel inlet. A plunger moves back and forth, thereby pumping fuel from the inlet chamber into a compression chamber.
The plunger downwardly moves in an intake stroke to draw fuel from the inlet chamber into the compression chamber. When an amount of fuel drawn from the inlet chamber into the compression chamber increases in the intake stroke, pressure in the inlet chamber may decrease. In particular, when an amount of fuel discharged from the high pressure pump increases, the plunger may be enlarged in diameter, or the reciprocating stroke of the plunger may increase. In these cases, an amount of fuel, which is drawn from the inlet chamber into the pressurizing camber, may increase. As a result, pressure in the inlet chamber is apt to decrease. In addition, when rotation speed of the high pressure pump increases, speed of reciprocating motion of the plunger increases. In this case, an amount of fuel, which is drawn from the inlet chamber into the compression chamber as the plunger downwardly moves, may exceed an amount of fuel introduced from the low pressure pump into the inlet chamber. As a result, pressure in the inlet chamber is apt to decrease.
In this condition, when pressure in the inlet chamber decreases in the intake stroke as the plunger downwardly moves, fuel may not be sufficiently drawn from the inlet chamber into the compression chamber. Consequently, an amount of fuel discharged from the high pressure pump may become insufficient.
Furthermore, when fuel returns from the compression chamber into the inlet chamber as the plunger upwardly moves, pressure in the inlet chamber may increase. As the plunger repeats reciprocating motion, pressure in the inlet chamber may fluctuate, and may cause pulsation. When an amount of fuel discharged from the high pressure pump increases, or when the number of rotation of the high pressure pump increases, pulsation of pressure in the inlet chamber may be further stimulated. In this condition, fuel may not be sufficiently drawn from the inlet chamber into the compression chamber when pulsation excessively arises in pressure in the inlet chamber. Accordingly, fuel may not be sufficiently supplied from the inlet chamber into the compression chamber. As a result, an amount of fuel discharged from the high pressure pump may be insufficient.